1. Field of the Invention
This invention relates to a magnetic powder for bonded magnets which is ready for injection molding when highly packed or filled, and also to a composition for bonded magnets and a method for preparing such a composition as mentioned above.
2. Description of the Related Art
As is known in the art, bonded magnets have been usually obtained by a procedure which comprises mixing a magnetic powder, such as a ferrite, with a binder such as nylons (polyamides), PPS (polyphenylene sulfide) or the like at an appropriate mixing ratio to obtain a mixture, kneading the thus obtained mixture by means of a kneader such as a KCK kneader, a biaxial extruder or the like, and subjecting the resultant bonded magnet composition in the form of pellets to injection extrusion molding. In order to have the bonded magnet imparted with a high magnetic force, attempts have been made to provide a bonded magnet composition wherein a magnetic powder is highly packed in a binder. In prior techniques, when a magnetic powder is highly packed, the resultant composition is undesirably lower in fluidity. If such a highly packed composition whose fluidity is lower is subjected to injection molding, there arises the problem that the molding machine may suffer clogging in the barrel thereof or the composition may not be injected in the mold, thereby making the molding impossible. Thus, some limitation has been placed on the high packing of a magnetic powder in the bonded magnet composition, i.e. on the formation of a bonded magnet whose magnetic force is high.